Process for heating the head of an ingot of molten ferrous material



5 1959 I K o. R. GEBHARD 2,870,005

PROCESS FOR HEATING THE HEAD OF AN INGOT OF MOLTEN FERROUS MATERIALFiled June 27, 1956 PROCESS FOR HEATING THE HEAD OF AN INGOT OF MOLTENFERROUS MATERIAL Kurt O. R. Gebhard, Brooklyn, Pretoria, Transvaal,Union of South Africa, assignor to South African Iron and SteelIndustrial Corporation Limited, Pretoria, Transvaal, Union of SouthAfrica Application June 27, 1956, Serial No. 594,201

Claims priority, application Union of South Africa July 6, 1955 7Claims. (Cl. 7560) ferrous metallic material being heated by passingthrough said conduit, oxygen having atleast the concentration ofoxygen-enriched air, the mouth of the said conduit being immersed in themolten ferrous metallic material being heated.

Preferably the conduit is in the form of a pipe, and a preferredmaterial for the production ofthe pipe or an essential part thereof isaluminium or an alloy of aluminium with a metal generating large amountsof heat when oxidised, e. g. with magnesium and/ or silicon. Suitablealuminium-silicon alloys can be obtained by the production of clays, e.g. in an electric furnace. This material will be particularly desirablein most applications for economic reasons. 7

Other materials or metalloids yielding slag forming oxidation productsmay also be employed as conduit materials, e. g. magnesium or silicon oralloys thereof.

The aforesaid conduit materials ma, of course, also contain otherconstituents, usually in small amounts.

The reactions and heats generated in the oxidation of various elementsare as follows:

i (a) Examples of metals undergoing treatment (b) Examples of conduit orlance metal materials In general, the material employed for making theconduit or lance or serving as a substantial constituent thereof shouldon combustion generate per kilogram at least 3000 Kcals. more than theheat generated by oxidation of a kilogram of the metal undergoingtreatment. Materials are very suitable 1 kilogram of which on oxidationgenerates at least 6000 Kcals.

In order to obtain a sound casting in normal foundry practice, thefeeder heads are made so large that they amount to say, 35 percent toabout 40 percent of the finished Weight of the finished casting withconsequential losses. The feeder heads can be made much smaller, sayabout 15-20 percent of the finished casting, e. g. about 50 percentsmaller, if the iron in the feeder head United States PatenrO into thefeeder head by means of a combustible lance or other conduit inaccordance with the invention and sound castings are thus produced. Infoundry practice approximately only so much oxygen should be introducedas is required for oxidising the lance or conduit material.

The invention is also applicable to the casting of ingots, in particularof killed steel.

' As is known, the cavities formed at the top of freezing ingots ofkilled steelnormally called pipessubstantially decrease the usefulportion of the ingot cast. As a result, a certain percentage of thetotal steel made and teemed has to be returned for remelting, and sopart of the energy, labour, and other cost factors expended in making acertain quantity of steel is wasted.

The effect of pipe formationon the economy of steel making is so great,that many attempts have been made to avoid or decrease the extent ofpiping in killed steels. In all these attempts, the aim was to keep thetop of the ingot molten as long as possible, so that cavities, whichhave formed in the upper part of the ingotdue to shrinkage in the courseof freezing can be filled in again by molten steel from the top.

According to the known art, the ingot topcan be kept molten by eitherproviding a good insulation of the top part of the ingot mould, or byapplying heat from a gas burner or electrically. Where applicable,especially in the manufacture of special steels, these methods are wellestablished. In the mass production of commercial steels, the use ofpulverulent compositions which when ignited react with a strongexothermic reaction,

. moulds generally consist of two main parts, a lower part is overheatedby blowing oxygen or air rich in oxygen for receiving the bulk of thecasting and an upper usually tapering part, or feeder h ad, which iswell insulated against loss of heat to maintain the ingot top molten aslong as possible. The metal in the feeder head or a great part thereofis usually cut away. The portion cut off and discarded for reprocessingis termed the lost head. The so-called lost head usually amounts toabout 10 to 20 percent of the total ingot weight. If the feeder head ismade too small, not enough metal is available to prevent prematurefreezing and to fill any cavities 'which may form. As a result a narrowand deep piping may occur.

In accordance with the invention, piping in the casting of ingots fromsteel, in particular killed steel, can be avoided by passing oxygen or agas rich in oxygen by means of a conduit, pipe or lance, made of oressentially containing a combustible material as herein specified intothe molten metal at the ingot top thus superheating it to preventpremature freezing and avoiding or greatly decreasing the formation ofpipes.

This operation may be carried out with advantage in ingot moulds havingfeeder heads of conventional size, containing e. g. 10 to 20 percent byweight of the total ingot because in accordance with the invention agreat part of the said feeder head solidifies to a sound ingot, so thatoften little more than the slag at the top has to be cut away. I

In accordance with the invention, however, ingot moulds with a smallerfeeder head, say containing 6 to 10 percent of the weight of the ingotmay be employed. This has the advantage that a great proportion of soundingot material is obtainable.

According to another modification of the invention the occurrence ofpiping when casting steels, in particular, in killed steels can beavoided or decreased by superladle by treatment with oxygen or oxygenrich gas introduced by means of a combustible lance as herein specifiedand using the thus superheated steel for after-teeming.

The feeder head of the ingot mould used can also under thesecircumstances be kept much smaller, 'say 6 to percent in proportion tothe ingot weight than used in normal practice.

According to the invention, in teeming ingots of. killed steel, asuitable amount, e. g. 3 to 8 percent of'th'e steel is poured into aladle of suitable size and design and treated with a lance in accordancewith the invention; Care should be taken by adjustments as regards thecontent of carbon, manganese, silicon and other elements, and as regardsthe composition of the lance that the steel used for after-teeming haspractically the same chemical composition as the bulk of the ingot.

Any crusts that might already have formed on the surface of the ingotwill remelt and the cavities formed be filled in. Any piping which mightstill occur will not be considerable when using a smaller feeder head,because the shrinkage of only a small volume of steel is involved. Suchpiping will be confined to the very top of the ingot only. Thus the lossdue to piping in further processing is decreased to a small amount.

A sound casting is produced with a smaller lost head and, as a result,great economic advantages are achieved by better exploitation of thesmelting capacity and labour involved in cutting the lost heads.

The casting of an ingot of killed steel in accordance with the inventionand the advantages obtained will be further described in the followingcomparative example with reference to the accompanying drawings in whichFig. 1 is a longitudinal section through an ingot top in accordance withthe invention and Fig. 2 is a similar section through the top of aconventionally produced ingot.

A heat of a fully killed steel having an, analysis of approximately0.40% C, 0.10% Si, 0.60% Mn, 0.02% S and 0.03% P was teemed intoconventional 4.5 t. hot top ingots. One of the ingots was treated byburning with oxygen an aluminium lance of approximately 6 lbs. weightinserted into the molten steel in the ingot head. This ingot and anuntreated reference ingot were split longitudinally.

Referring now to the drawings, 1 indicates the ingot body and 2 theingot head. 3 (Fig. 2) indicates the boundaries of the piping in theconventional ingot. From free from such pipes. The black areas 4indicate blow holes and cavities present in the ingots. It will be seenthat these occur to a much smaller extent in the ingot in accordancewith the invention than in the reference ingot and in the treated ingot,they occur only to a small depth from the surface. It canbe clearly seenthat the losses by cropping required for the untreated ingotare muchhigher than for the treated ingot. It was found that on the untreatedingota loss of approximately 7 percent of the total ingot weightoccurred, whilst on the treated ingot 3.5 percent only were lost.Practical experience has shown that on untreated ingots the loss isnormally in the range of 10 percent, so that the actual savings arestill greater than shown on the experiment.

What I claim is:

1. A process for heating the head of an ingot of molten ferrous materialcomprising introducing into the head a metal conduit of solidcombustible material having an exothermic reaction heat substantiallygreater than that of the ferrous material, passing an oxidizing gasthrough the conduit, and oxidizing the conduit in the head of the ingot.

2. A process as claimed in claim 1 wherein the conduit is of a materialselected from the group consisting of Al, Si and Mg and combinationsthereof.

3. A process as claimed in claim 1 wherein said mentioned material has areaction heat of at least 6000 Kcal. per kilogram.

4. A process as claimed in claim 1 wherein the gas is oxygen-enrichedair.

5. A process as claimed in claim 1 wherein the conduit is progressivelyfed into the head of the ingot to compensate for the oxidizing of theconduit.

6. A process as claimed in claim 1 wherein the ferrous materialconstitutes the ingredients of killed steel.

7. A process as claimed in claim 1 wherein the conduit is oxidized to aslag.

References Cited in the file of this patent UNITED STATES PATENTS937,163 Mesta Oct. 19, 1909 968,350 Harrison Aug. 23, 1910 1,494,003Malcher May 13, 1924 2,286,191 Aitchison et al June 16, 1942 2,491,440Boedecker et a1. Dec. 13, 1949 2,502,259 Hulme Mar. 28, 1950 FOREIGNPATENTS 673,605 Great Britain June 11, 1952 696,840 Great Britain Sept.9, 1953

1. A PROCESS FOR HEATING THE HEAD OF AN INGOT OF MOLTEN FERROUS MATERIALCOMPRISING INTRODUCING INTO THE HEAD A METAL CONDUIT OF SOLIDCOMBUSTIBLE MATERIAL HAVING AN EXOTHERMIC REACTION HEAT SUBSTANTIALLYGREATER THAN THAT OF THE FERROUS MATERIAL, PASSING AN OXIDIZING GASTHROUGH THE CONDUIT, AND OXIDIZING THE CONDUIT IN THE HEAD OF THE INGOT.